title: Axial iron coordination and spin state change in a heme c upon electrostatic protein-SAM interaction.
abstract: A bacterial di-heme cytochrome c binds electrostatically to a gold electrode surface coated with a negatively charged COOH-terminated SAM adopting a sort of 'perpendicular' orientation. Cyclic voltammetry, Resonance Raman and SERRS spectroscopies indicate that the high-potential C-terminal heme center proximal to the SAM's surface undergoes an adsorption-induced swapping of one axial His ligand with a water molecule, which is probably lost in the reduced form, and a low- to high-spin transition. This coordination change for a bis-His ligated heme center upon an electrostatically-driven molecular recognition is as yet unprecedented, as well as the resulting increase in reduction potential. We discuss it in comparison with the known methionine ligand lability in monoheme cytochromes c occurring upon interaction with charged molecular patches. One possible implication of this finding in biological ET is that mobile redox partners do not behave as rigid and invariant bodies, but in the ET complex are subjected to molecular changes and structural fluctuations that affect in a complex way the thermodynamics and the kinetics of the process.
authors.affiliation: Department of Life Sciences, University of Modena and Reggio Emilia, Via Campi 183, I-41125 Modena, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Di Rocco
authors.forename: Antonio
authors.initials: A
authors.lastname: Ranieri
authors.forename: Carlo Augusto
authors.initials: CA
authors.lastname: Bortolotti
authors.forename: Gianantonio
authors.initials: G
authors.lastname: Battistuzzi
authors.forename: Alois
authors.initials: A
authors.lastname: Bonifacio
authors.forename: Valter
authors.initials: V
authors.lastname: Sergo
authors.forename: Marco
authors.initials: M
authors.lastname: Borsari
authors.forename: Marco
authors.initials: M
authors.lastname: Sola
mesh_terms: D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism; D004566:Electrodes; D006046:Gold / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D020592:Shewanella / Q000201:enzymology; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D006046:Gold; D045304:Cytochromes c; D007501:Iron